The present invention relates to a method and apparatus for manipulating stacks of paper sheets or the like, and more particularly to improvements in a method and apparatus for introducing stacks of normally flexible sheets into prefabricated cartons or other types of receptacles. Still more particularly, the invention relates to improvements in a method and apparatus for introducing successive stacks of a series of stacks into successive receptacles of a series of receptacles while the receptacle which is about to receive a stack dwells in or close to a predetermined position, i.e., at a predetermined location.
It is well known to fill receptacles (e.g., cardboard boxes of the type known as cartons) with sheets of paper or the like by accumulating the sheets into stacks which are thereupon delivered to a carton filling station and dropped into the respective receptacles. Thus, each stack is advanced to a position of register with the open top of a receptacle and is thereupon caused or allowed to descend by gravity so as to enter the receptacle therebelow. The freshly filled receptacle is removed from the predetermined position, provided with a cover or lid, and transported to storage or to a further processing station. Successive empty receptacles are delivered by a first conveyor, and the stacks are delivered by a second conveyor whose discharge end is located at a level above a portion of the path which is defined by the first conveyor. The stack which reaches the position of registry with a carton therebelow is supported by a platform which is removable so that the stack can descend by gravity to drop into the carton therebelow. The platform may consist of or may include two flaps which are pivotable between substantially horizontal positions to support a stack from below and second positions in which they extend downwardly. Alternatively, the flaps can be retracted laterally so that the stack can descend therebetween. Reference may be had to German Offenlegungsschrift No. 2,756,473 which discloses laterally shiftable flaps. Once a stack has been allowed to descend by gravity, the flaps return to their operative (intercepting) positions to support the next-following (oncoming) stack, and the freshly filled carton below the flaps is replaced with an empty carton.
A drawback of the just outlined conventional methods and apparatus is that the stacks must be delivered to a location other than the receptacles prior to actual introduction into the receptacles. This takes up substantial amounts of time ad necessitates resort to additional equipment, such as the aforementioned platform with laterally retractable or downwardly pivotable flaps, panels or like components. Moreover, gravitational descent of stacks into cartons or analogous receptacles through the open tops of the receptacles invariably involves the danger of misalignment of stacks or certain sheets of stacks during descent into the receptacles therebelow, shifting of one or more layers of the stacks with reference to the remaining layer or layers, and/or damage to or deformation of the receptacles. The likelihood of damage to the stacks, to the receptacles, to stacks and receptacles and/or shifting of some layers or sheets of a stack relative to the other layers or sheets is especially pronounced when the stacks are to be introduced into receptacles whose dimensions practically match or only slightly exceed the dimensions of the respective stacks. It is quite customary to utilize receptacles in the form of thin-walled and therefore relatively unstable cartons which are likely to undergo deformation, either during transport to a position below a stack which is about to descend and/or during introduction of the stack by gravity, if the stack is not in exact register with the carton therebelow. Bulging of side walls of a carton which is open at the top causes the corners of such carton to move inwardly and to be located in the path of a descending stack. The stack is incapable of entering the thus deformed carton and causes additional deformation of the carton as a result of impingement of its lowermost sheet or sheets against the inwardly drawn corners.
Additional problems arise in connection with the manipulation of stacks which are assembled of large or very large sheets. Such stacks are especially likely to be deformed during gravitational descent into the receptacles therebelow. The deformation normally entails at least some shifting of the upper layer or layers relative to the lower layer or layers and/or vice versa. The likelihood of shifting of layers relative to each other is even more pronounced when the stacks are assembled of lightweight sheets.